Ninety-nine million years ago, a 55-foot dinosaur crept across the river deltas of North Africa. A sail on his back towered over the water, while his crocodile-like jaws and curved claws made short work of fish from a car.
It was Spinosaurus, discovered in 1915. Paleontologists have since debated how this creature lived. Did it float through the streams in pursuit of prey, as recent research has suggested, or did it search the quarry in the plain, more like an enormous wader? New evidence for this second statement was published in Palaeontologia Electronica on Tuesday, challenging a hypothesis that scientists have found a dinosaur that lives primarily in aquatic life.
The idea that spinosaurus spent most of its time underwater has been driven in recent years by the announcement in 2014 by Nizar Ibrahim, a paleontologist at the University of Portsmouth in England, and colleagues of their discovery of a partial skeleton of the predator. They argued that it spent much of its time underwater, the first dinosaur known for it. The idea was strengthened last year when the team of dr. Ibrahim announced the discovery of a fin-like, eel-like spinosaur tail.
The case for a more aquatic spinosaurus rests on some peculiar features, said dr. Ibrahim said. Unlike most predatory dinosaurs – including some family members such as the tortuous baryonyx – spinosaurus has densely mineralized bones, extremely short hind limbs, and a tail configuration that allowed for tortuous, shell movements.
“Really, on every part of the body we looked at, ‘water-loving’ was written about,” said Dr. Ibrahim said.
Other paleontologists have raised doubts about this hypothesis.
“True pursuit of water in pursuit of water is a very challenging lifestyle,” said Thomas Holtz Jr., a predator dinosaur specialist at the University of Maryland and co-author of the new article. Water predators such as otters, sea lions or sharks have compact, smooth bodies that reduce underwater resistance.
According to David Hone, a paleontologist at the Queen Mary University of London and co-author with dr. Holtz, did earlier research by dr. Ibrahim’s team showed that spinosaurus has a relatively small number of tail muscles, dr. Hone said, even less so than crocodiles, which also tend to have problems with towing and are not very efficient at chasing prey underwater. With its long sail and voluminous limbs, spinosaurus would have produced tremendous resistance in all but the deepest water, making rapid sub-aquatic pursuits extremely difficult.
Instead, the team points to a different set of characteristics. Spinosaurus had nostrils on its long snout, like a hedgehog, dr. Hone said, rather than on top of his face, like a crocodile. It had broad feet, like a stork, as well as a head and neck adapted for a strong downward strike. Isotopic evidence of spinosaurus status also suggests that at least some individuals ate fully terrestrial prey, perhaps other dinosaurs as well.
Without further spinosaurus remains, it is difficult to see what differences could exist between animals of different ages or sexes, said dr. Holtz said. Several species of dinosaurs changed drastically as they grew: young tyrannosaurs were predators that were quickly chased, while adults were beaks. More fossils would help determine “whether the tail sails were mostly visible rather than moving forward (for example, if males had long sails and females had more normal sails), or that different growth stages had more water adaptations than others,” he said. said. email.
But in light of the available anatomical evidence, dr. Hone said, it seems like spinosaurus is better suited for crawling along the shore, like blowing out a heron to snatch prey or swimming on the surface and descending to lure fish underneath.
‘“The idea that spinosaurs hang out by the water is not controversial,” he said. ‘We are not saying that it did not swim, or even swam relatively well. But the idea that it is an otter-like animal probably goes too far. ‘
Dr. Ibrahim said that although he welcomed the debate, he and his team kept their earlier findings on spinosaurus was better adapted to underwater hunting than any other known dinosaur, and probably targeted large, slow-moving fish as well as rural prey.
“There is really nothing in this article that we have not considered before, which is not too surprising since no new data is being contributed, such as new fossil remains or quantitative analyzes and experiments,” he said.
Some paleontologists believe that aspects of dr. Ibrahim’s earlier findings can be integrated into the hypothesis that spinosaurs were forefathers.
“The hedgehog model at this time is the simplest statement that fits the available data, and in our science it is often the best way to follow,” said Serjoscha Evers, a spinosaur specialist at the University of Friborg in Switzerland. . paper.